1. Field of the Invention
The present invention relates to a reaction control system for controlling a reactive force to be applied to an operating device in a steering system of a vehicle.
Priority is claimed on Japanese Patent Application No. 2004-204523, filed Jul. 12, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
As a steering system for a vehicle, an electric power steering system is known. In the electric power steering system, a steering shaft coupled to a steering wheel is mechanically coupled to a steering mechanism for steering steered wheels, and an electric motor for assisting steering power is linked to the steering mechanism. In such an electric power steering system, a driving torque command value for the electric motor (i.e., a current value of current for driving the motor) is controlled in a manner such that the greater the steering torque applied to the steering shaft, the greater the assistant steering power is.
In an example system of the electric power steering system, a base driving torque command value is determined according to the steering torque of the steering wheel, and the driving torque command value is determined by subtracting a driving torque correction value, which is determined according to the steering speed of the steering wheel, from the base driving torque command value (see, for example, Japanese Patent No. 3176899). The driving torque correction value indicates a reactive force for the driving torque command value (which is an assistant power component), and functions for applying steering reaction (force) to the steering wheel.
However, in the conventional system in which the driving torque correction value is determined according to the steering speed of the steering wheel, when a steered state is maintained or steering in the opposite direction (i.e., a returning operation) is performed and the steering speed becomes zero, the driving torque correction value indicating the reactive force also becomes zero (i.e., the steering reaction of the steering wheel becomes zero); thus, it is difficult to obtain sufficiently stable feeling for the steering wheel while the steered state is maintained, and hysteresis for returning the steered wheels is low, thereby degrading steering feeling.